This invention relates generally to devices and methods for remotely detonating one or move explosive charges.
More specifically this invention relates to the precisely timed, remote detonation of explosive charges using electrical detonators in environments having high levels of extraneous electricity including stray ground currents, electromagnetic fields and radio frequency energy.
It has become increasingly common for hostages to be taken during criminal activity or in the commission of terrorist acts. Concern for the safety of hostages has ordinarily inhibited or precluded the use of force by the responsible authorities. When force is employed, it is necessary to act with precise timing so as to prevent, or minimize, any retaiatory action on the part of the terrorists toward the hostages.
In many instances, any effective response by the authorities requires the use of explosives, as for example, to breach a wall, to sever the hinges or lock of a door, to create a diversion, to disperse smoke or disabling gases, or for other analogous purposes. Ordinarily, a number of different types or sizes of explosive devices situated at different locations are desirably employed. There are immense practical difficulties involved in the physical placement of explosive devices under such conditions and the time that might be required to accomplish such placement is ordinarily difficult to predict. Also, hostage-taking events often display rapidly changing circumstances. Consequently, it is impractical and frequently undesirable to place an explosive charge having a fixed, or preset, time of detonation.
The remote detonation of explosive charges is, of course, well known and commonly practiced in commercial and industrial blasting. Explosive charges are most commonly detonated using electric blasting caps as initiators. Non-electric blasting caps for use with safety fuse and detonating cord are also routinely used explosive charge initiators.
None of these conventional techniques for detonating explosive charges is satisfactory for use in terrorist situations. Most terrorist acts and hostage-taking events occur in urban and highly congested areas. Such areas normally contain high levels of extraneous electricity, especially stray ground currents, electromagnetic fields associated with transmission lines, and radio frequency energy from TV and radio transmission and the like. This background electrical energy is ordinarily substantially increased by the high concentration of communications and surveillance devices which converge on the area in response to a terrorist act. It is well known that radio frequency current induced in a blast wiring circuit can initiate electric blasting caps. Consequently, safety considerations require that electric blasting not be attempted in areas where extraneous currents are greater than about 50 milliamperes.
When extraneous currents exceed about 50 milliamperes, standard safety precautions require use of a non-electric initiating system. Those non-electric systems comprising blasting caps and safety fuse are time consuming to rig and, after being rigged, are quite inflexible. It is, for example, difficult to change the sequence of detonation, to precisely control the timing of detonation, and to change the time delay between individual charges. Also, there is a finite time delay between ignition of the fuse and detonation of the corresponding explosive charge.
Because of the safety, environmental and timing requirements and restraints placed upon explosives use in terrorist and hostage-taking events, conventional blasting techniques are of little value. Yet, the judicious use of explosives offers a very effective tool in suppressing terrorist activities.